The present invention provides rubber mixtures with improved processing behavior containing special polyethers and use of the rubber mixtures for preparing vulcanizates, in particular for the production of highly reinforced, abrasion-resistant molded items, preferably for producing tires which have a low rolling resistance and a high abrasion resistance.
A number of solutions have been put forward for producing tires with low rolling resistance. Certain polysulfidic silanes are described in DE-A-2 255 577 and 4 435 311. EP-A1-0 670 347 and U.S. Pat. No. 4,709,065 as reinforcement additives for silica-containing rubber vulcanizates. The disadvantage of using the polysulfidic silanes described in those patents as reinforcement additives for silica-containing rubber vulcanizates, however, is that relatively large amounts of the expensive polysulfidic sulfides are required in order to achieve acceptable processability.
To improve the processability of silica-containing rubber mixtures, other additives have been suggested such as esters of fatty acids, salts of fatty acids or mineral oils. The additives mentioned have the disadvantage that they increase the ability to flow, but also reduce the modulus at high extensions (e.g., 100 to 300%) so that the reinforcing effect of the filler suffers a decrease.
In addition, it is known that polyalcohols and polyglycols can be added to rubber mixtures. Thus, EP-A1-0 869 145 and EP-A1-0 738 755 describe rubber mixtures which contain certain polyethylene oxides. The special structures of the polyethers according to the present invention were not disclosed. According to the disclosure in these documents, the polyethylene oxides mentioned barely improve the processability of the unvulcanized rubber mixtures at all but act mainly on the vulcanizate properties, in particular on the antistatic properties and on the abrasive behavior.
Thus, the object of the invention was to provide additives, which improve the ability of rubber mixtures to flow and yield vulcanizates with improved properties, in particular with respect to abrasion, rolling resistance and wet skid resistance in the case of tires.
Special polyethers were found which, surprisingly, clearly improve the ability of rubber mixtures to flow and lead to vulcanizates with good reinforcement characteristics, favorable dynamic damping and good abrasion characteristics.
Therefore, the present invention provides rubber mixtures containing in the range from 0.05 to 25 parts by wt., with respect to 100 parts by wt. of the total amount of rubber used, of a polyether of the structure (I) 
in which
R1 and R2, independently, represent hydrogen or a C1 to C4 alkyl group and
R3 and R4, independently, represent hydrogen or a C1 to C6 alkyl group and
R5 and R6, independently, represent hydrogen, a C1 to C18 alkyl group, a C7 to C22 alkylaryl group, a C7 to C22 arylalkyl group, the group xe2x80x94CH2xe2x80x94OH or the group xe2x80x94CHR4xe2x80x94(xe2x80x94Oxe2x80x94CHR1xe2x80x94CHR2xe2x80x94)mxe2x80x94OH, with the condition that at least one of the groups R5 and R6 is a C1 to C18 alkyl group, a C7 to C22 alkylaryl group or a C7 to C22 arylalkyl group, and
n and m, independently, represent integers from 1 to 10, preferably 1 to 5, and also in the range from 1 to 500 parts by wt. of filler and optionally other rubber auxiliary substances and/or cross-linking agents.
Preferred representatives of polyethers (I) are addition and polyaddition compounds of neopentyl glycol or trimethylolpropane within the range from 0.7 to 10 mol of ethylene oxide and/or propylene oxide per hydroxyl group with molecular weights in the range from 192 to 1,500, preferably in the range from 192 to about 700. The addition and polyaddition compounds of in the range from 0.7 to 7 mol of ethylene oxide and/or propylene oxide per mol of hydroxyl groups in neopentyl glycol or trimethylolpropane are preferred, and the corresponding addition and polyaddition products of in the range from 0.7 to 3 mol of ethylene oxide and/or propylene oxide per hydroxyl group in trimethylolpropane are most preferred.
The preparation of these types of addition and polyaddition products is part of the prior art (Houben-Weyl, Methoden der organischen Chemie, vol. XIV/2, Thieme Verlag, Stuttgart, 1963, pages 436-440, 450). These types of polyethers are also commercially available. Suitable polyethers are, for example, Desmophene(copyright) 550 U and Desmophen(copyright) 4011 T from Bayer AG. The polyethylene oxides and polypropylene oxides or their mixed polyethers are preferably used as mixtures due to the method of preparation.
An amount in the range from 0.3 to 15 parts by wt., preferably 1 to 10 parts by wt., with respect to 100 parts by wt. of the total amount of rubber used, of polyether (I) is added to rubber mixtures according to the present invention.
The rubbers to be used to prepare rubber mixtures according to the present invention include natural rubber and synthetic rubbers. Preferred synthetic rubbers are described, for example, in W. Hofmann, Kautschuktechnolgie, Genter Verlag, Stuttgart, 1980. They include, inter alia,
BR polybutadiene
ABR butadiene/C1-C4-alkyl acrylate copolymers
CR polychloroprene
IR polyisoprene
SBR styrene/butadiene copolymers with styrene contents in the range from 1-60, preferably in the range from 20-50, wt. %
IIR isobutylene/isoprene copolymers
NBR butadiene/acrylonitrile copolymers with acrylonitrile contents in the range from 5-60, preferably in the range from 10-40, wt. %
HNBR partly hydrogenated or fully hydrogenated NBR rubbers
EPDM ethylene/propylene/diene copolymers
and mixtures of these rubbers.
Mixtures of natural rubber, emulsion SBR and solution SBR and polybutadiene rubbers are important for the production of motor vehicle tires. Of particular interest for use in rubber mixtures according to the present invention is the use of solution SBR rubbers with a vinyl content in the range from 20-60 wt. % and of polybutadiene rubbers with a high 1,4-cis content ( greater than 90%), which have been prepared with catalysts based on nickel, cobalt, titanium and/or neodymium, and also polybutadiene rubbers with a vinyl content of up to 75% and mixtures of the solution SBR and polybutadiene rubbers mentioned. Most preferred are the corresponding solution SBR and polybutadiene rubbers with an additional concentration of bonded functional groups, in particular hydroxyl and/or carboxyl groups. Preferred concentrations of hydroxyl and/or carboxyl groups are in the range from 0.05 to 3 wt. %, with respect to the rubber. Most preferred rubbers according to the present invention are described, for example, in German patent applications DE-A1-198, 32 549, DE-A1-198 52 648, DE-A1-1 99 14 848, DE-A1-199 20 788, DE-A1-199 20 814 and DE-A2.653.144 and EP-A1-0 464 478, which are included in the application, as reference material, for US practice.
Rubber mixtures according to the present invention can contain in the range from 0.1 to 300 parts by wt. of a wide variety of fillers, with respect to 100 parts by wt. of the total amount of rubber. Suitable fillers are mainly oxidic and/or silicate fillers and/or carbon black. Oxidic and/or silicate fillers are preferred.
The following are most preferred:
highly dispersed silica, prepared, for example, by precipitation from solutions of silicates or flame hydrolysis of silicon halides with specific surface areas in the range from 5 to 1000, preferably in the range from 20-400 m2/g (BET surface area) and with primary particle sizes in the range from 10-400 nm. The silicas can optionally also be present as mixed oxides with other metal oxides such as Al, Mg, Ca, Ba, Zn, Zr, Ti, oxides.
synthetic silicates such as aluminum silicate, alkaline earth silicates such as magnesium silicate or calcium silicate, with BET surface areas in the range from 20-400 m2/g and primary particle diameters in the range from 10-400 nm.
natural silicates such as kaolin and other naturally occurring silicas.
glass fibers and glass fiber products (mats, ropes) or glass microbeads.
metal oxides such as zinc oxide, calcium oxide, magnesium oxide, aluminum oxide.
metal carbonates such as magnesium carbonate, calcium carbonate, zinc carbonate.
metal hydroxides such as aluminum hydroxide, magnesium hydroxide.
The fillers mentioned are preferably used in amounts in the range from 5 to 200 parts by wt., more preferably in the range from 10 to 150 parts by wt., with respect to 100 parts by wt. of the rubber used.
As mentioned, carbon blacks are also suitable as fillers. They are prepared by the lamp black, furnace black or channel black process and generally have BET surface areas of 20 to 200 m2/g, such as SAF, ISAF, HAF, FEF or GPF carbon blacks.
In a most preferred embodiment, rubber mixtures according to the present invention comprise, in addition to at least one rubber, of from 0.5 to 10 parts by wt. of polyhydroxyl compound (I), from 10 to 100 parts by wt. of oxidic or silicate fillers and from 5 to 50 parts by wt. of carbon black, each with respect to 100 parts by wt. of the rubber used.
To prepare rubber vulcanizates, known and conventionally used rubber auxiliary products may be added to rubber mixtures according to the present invention, in particular vulcanization accelerators, antioxidants, heat stabilizers, light protection agents, anti-ozone agents, processing auxiliary substances, plasticizers, tackifiers, blowing agents, colorants, pigments, waxes, extenders, organic acids, delayers, metal oxides, cross-linking agents and activators, In this connection, reference is made to I. Franta, Elastomers and Rubber Compounding Materials, Elsevier 1989, p. 325-494.
The rubber auxiliary agents are used in conventional amounts, which are governed, inter alia, by the ultimate use. Conventional amounts are in the range from 0.1-50 wt. %, with respect to the total amount of rubber used.
In addition, known cross-linking agents such as sulfur, sulfur donors or peroxides can also be used during preparation of the rubber vulcanizates. In addition, vulcanization accelerators such as mercapto-benzthiazoles, guanidines, thiurams, dithiocarbamates, thioureas and/or thiocarbonates may obviously also be added to rubber mixtures according to the present invention. Vulcanization accelerators and cross-linking agents are used in amounts in the range from 0.1-10 wt. %, preferably in the range from 0.1 to 5 wt. %, with respect to the total amount of rubber used.
In a preferred embodiment, rubber mixtures according to the present invention also contain, in addition to the rubbers mentioned, fillers, polyethers (I), rubber auxiliary agents and cross-linking agents, in the range from 0.2 to 4 parts by wt. of zinc salts of aliphatic, cycloaliphatic and/or aromatic C6-C36 carboxylic acids, e.g. zinc salts of tallow fatty acid, oleic acid or benzoic acid. In addition, in the most preferred embodiment, in the range from 0.5 to 15 parts by wt., with respect to 100 parts by wt. of rubber used, of sulfur-containing silyl ethers are also added as filler activators, in particular bis-(trialkoxysilyl-alkyl)-polysulfides as described in DE-A-2 141 159 and DE-A-2 255 577, oligomeric and/or polymeric sulfur-containing silyl ethers as described in DE-A-4 425 311 and EP-A1-0 670 347 and also mercapto.-alkyltrialkoxysilanes, mercaptopropyltriethoxysilane and/or thiocyanatoalkylsilyl ethers as described in DE-A-1 95 44 469.
Rubber mixtures according to the present invention can be prepared using conventional equipment such as mixing units, in particular rollers, internal mixers and mixer-extruders.
Vulcanization of rubber mixtures according to the present invention can be performed conventionally at temperatures in the range from 100 to 200xc2x0 C., preferably in the range from 130 to 180xc2x0 C., optionally at pressures in the range from 10 to 200 bar.
Rubber mixtures containing polyethers (I) according to the present invention are characterized, in particular, by a particularly high ability to flow, high processing reliability, and improved vulcanization kinetics and provide vulcanizates with relatively high values for the modulus. They are, therefore, suitable in particular for the cost-effective production of highly reinforced, abrasion-resistant molded items.
The following may be mentioned, in particular, as molded items: cable sheathing, hoses, drive belts, conveyer belts, roller coverings, tires, soles of shoes, sealing rings and damping elements. Most preferred is the use of rubber mixtures according to the present invention for the production of tire treads with low rolling resistance.